Solar power generation systems for generating solar power in which solar cell modules, each including a plurality of solar cell strings arranged in a matrix, are placed on the roof of buildings or the like are beginning to come into wide use. In such a solar cell power generation system, each solar cell module is provided with a terminal box for enabling an electrical connection with another solar cell module placed adjacent to the solar cell module.
An example of a configuration of a solar cell string constituting a conventional solar cell module is shown in FIGS. 23(a) and 23(b) and FIG. 24. FIGS. 23(a) and 23(b) are illustrative diagrams showing two scenes of a manufacturing process thereof, and FIG. 24 is an illustrative diagram showing a step of laminating and sealing a solar cell string. The example of the configuration of the solar cell string shown in FIGS. 23 and FIG. 24 is also described in Patent Document 1.
A solar cell 115 is formed by laminating, although not shown in the drawings, a transparent electrode film made of a transparent conductive film, a photoelectric conversion layer and a back face electrode film in this order on a light-transmitting insulating substrate 111.
The solar cell 115 thus configured has, as shown in FIG. 23(a), an elongated rectangular shape with a length extending substantially across the entire width of the light-transmitting insulating substrate 111. A solar cell string 116 in which a plurality of solar cells 115 are connected in series is configured by connecting the transparent electrode film of one of each two adjacent solar cells 115 and the back face electrode film of the other solar cell to each other.
On an end of the transparent electrode film of the solar cell 115 located at one end of the solar cell string 116, a P-type electrode terminal portion 117 having a linear shape with substantially the same length as the solar cell 115 is formed, and on an end of the back face electrode film of the solar cell 115 located at the other end of the solar cell string 116, an N-type electrode terminal portion 118 having a linear shape with substantially the same length as the solar cell 115 is formed. The P-type electrode terminal portion 117 and the N-type electrode terminal portion 118 serve as electrode lead-out portions.
An insulating sheet 119 is placed on the solar cell string 116 so as to extend between a center area of the P-type electrode terminal portion 117 and a center area of the N-type electrode terminal portion 118. The insulating sheet 119 is placed such that it does not overlap the P-type electrode terminal portion 117 and the N-type electrode terminal portion 118. The insulating sheet 119 is preferably a film compatible to a sealant, and in particular, it is optimal to use a PET film, a fluorocarbon resin film or the like. In order to ensure the adhesion of the insulating sheet, a resin sheet for bonding may be placed between the insulating sheet 119 and the solar cells 115 or between the insulating sheet 119 and a lead wire 112 or 113, or these may be bonded in advance with an adhesive or the like.
On the other hand, a positive electrode current collecting portion 120 called bus bar and made of a copper foil having the same shape and size as the P-type electrode terminal portion 117 is electrically and mechanically bonded to the entire face of the P-type electrode terminal portion 117. Likewise, a negative electrode current collecting portion 121 having the same shape and size as the N-type electrode terminal portion 118 is electrically and mechanically bonded to the entire face of the N-type electrode terminal portion 118. As a means for bonding these, soldering or a conductive paste can be used, for example.
A positive electrode lead wire 122 and a negative electrode lead wire 123 that are made of flat cables are disposed in line (or parallel, i.e., disposed offset in the width direction) on the insulating film 119, with their tips opposing each other.
One end of the positive electrode lead wire 122 is connected to a center position of the positive electrode current collecting portion 120. The other end of the positive electrode lead wire 122 is located in a substantially center area of the solar cell string 116, and is bent so as to stand upright from the face of the solar cell string 116 (for example, perpendicularly with respect to the face) to serve as an output lead portion 122a. Likewise, one end of the negative electrode lead wire 123 is connected to a center position of the negative electrode current collecting portion 121. The other end of the negative electrode lead wire 123 is located in a substantially center area of the solar cell string 116, and is bent so as to stand upright from the face of the solar cell string 116 (for example, perpendicularly with respect to the face) to serve as an output lead portion 123a. 
Although the positive electrode lead wire 122 and the negative electrode lead wire 123 extend across a plurality of solar cells 115, the insulating sheet 119 is present between the lead wires and the solar cells 115, and therefore the solar cells 115 will not be short-circuited. It is desirable that the width of the insulating sheet 119 is sufficiently larger than the width of the positive electrode lead wire 122 and the negative electrode lead wire 123, and the insulating sheet 119 is disposed in the form of a belt-like sheet extending from the positive electrode current collecting portion 120 to the negative electrode current collecting portion 121.
In this state, as shown in FIG. 24, a sealing film 124 and a back film 125 serving as a back face protection material for weather resistance and high insulation are laminated and sealed on the entire face of the solar cell string 116, with the output lead portions 122a and 123a of the positive electrode lead wire 122 and the negative electrode lead wire 123 passing through openings 124a and 125a. The sealing film 124 is preferably a thermoplastic polymer film, and in particular, it is optimal to use a film made of EVA (ethylene vinyl acetate resin) or PVB (polyvinyl butyral resin). The back film 125 is preferably, in order to ensure moisture resistance, a film including a moisture resistant layer such as a three-layer structure film of PET/Al/PET (PET: polyethylene terephthalate) or a three-layer structure film of PVF/Al/PVF (PVF: polyvinyl fluoride resin film).
In the solar cell string 116 thus configured, a terminal box (not shown) is attached and electrically connected to the output lead portions 122a and 123a of the positive electrode lead wire 122 and the negative electrode lead wire 123 protruding upward from the openings 125a of the back film 125.
When an opening 125a is formed in the three-layer structure back film 125 by punching or the like, the Al layer is exposed at the end face of the opening 125a. Accordingly, the distance between the exposed end face of the Al layer and the back electrode film of the solar cell 115 is shortened, and an electrical discharge may result when a dielectric strength test is performed. In particular, recent solar cell modules have increased voltages and require high voltages as dielectric strengths, and thus the above structure has a high possibility of occurrence of accidents caused by an electrical discharge.
Also, other than the dielectric strength between the end face of the Al layer of the back film 125 and the back face electrode film, the solar cell module having the above configuration has another problem in that there is a possibility that each opening 125a of the back film 125 might come into contact with the output lead portion 122a, 123a. In other words, because there is nothing to fix the opening 125a and the output lead portion 122a, 123a in a relative positional relationship between them, depending on the bending angle of the output lead portion 122a, 123a, the output lead portion 122a, 123a may come into contact with the opening 125a of the back film 125. If the output lead portion 122a, 123a comes into contact with the opening of the back film 125, the output lead portion 122a, 123a will come into contact with the end face of the Al layer of the opening 125a, and the two lead wires 122 and 123 of different polarities may be short-circuited. To address this, attempts have been heretofore made to prevent such short-circuiting between the output lead portion 122a, 123a and the end face of the opening 125a (see, for example, Patent Document 2).
Patent Document 2 discloses a thin film solar cell module having a structure in which, as shown in FIGS. 5(D) and 6(E) of Patent Document 2, a tedler sheet piece having slits which are slightly larger than holes of a protective cover is set around solder-plated copper foils (the output lead portions 122a and 123a in the above-described configuration) on a filler sheet, an EVA sheet piece 12 having substantially the same size is set, and the back face protective cover is set the EVA sheet piece 12. Then, the solder-plated copper foils are caused to project through the openings of the back face protective cover and fixed, using a heat resistant tape, in such a position that each copper foil and the back face protective cover will not come into contact with each other. Therefore, the sheets will not shift out of position relative to each other during a vacuum laminating step, and thus short-circuiting will not occur.